my $fn =
        ($ENV{NIX_LOG_DIR} || "/nix/var/log/nix") . "/drvs/"
        . substr($base, 0, 2) . "/"
        . substr($base, 2);
    return $fn if -f $fn;
    $fn .= ".bz2";
    return $fn if -f $fn;

    my $bucketed = substr($base, 0, 2) . "/" . substr($base, 2);
    my $fn = ($ENV{NIX_LOG_DIR} || "/nix/var/log/nix") . "/drvs/";
    for ($fn . $bucketed . ".bz2", $fn . $bucketed, $fn . $base . ".bz2", $fn . $base) {
        return $_ if (-f $_);
    }